The present invention relates to an electron energy loss spectrum measuring apparatus, a transmission electron microscope or a scanning transmission electron microscope, and an electron energy loss spectrum measuring method.
As semiconductor devices and magnetic head elements become small and microscopic, the elements has a structure where thin films of several nm (nanometer) are laminated in an area of about submicron. Since the structure, the element distribution, the crystal structure, and the chemical bonding state of the micro area largely affect characteristics of the semiconductor elements and the magnetic head elements, it is important to analyze the micro area.
Methods for observing the micro area include a scanning electron microscope (SEM), a transmission electron microscope (TEM), and a scanning transmission electron microscope (STEM). The TEM and the STEM have a spatial resolution at nanometer level. The TEM is an apparatus which irradiates an electron beam almost parallel to a specimen, and magnifies the transmitted electron beam with a lens or the like. On the other hand, the STEM converges an electron beam into a micro area, measures the transmitted electron beam while scanning the electron beam in two dimensions on a specimen, and obtains a 2D image.
An energy loss specific to an element (electron structure) is generated by an interaction with the elements constituting a specimen when an electron beam transmits through the specimen in the TEM and the STEM. Electron energy loss spectroscopy (EELS) uses an electron spectrometer to apply an energy analysis to electrons which have transmitted through the specimen, and is an analyzing method which can analyze elements in the specimen. A difference in chemical bonding state of identical elements especially reflects the electron structure of the element, and is appears as an energy shift at a level of a few eV. As a conventional analyzing apparatus, the TEM or the STEM combined with an electron energy loss spectrometer (EELS) of parallel detection type is widely used.
An electron beam transmits through a specimen, passes through an objective lens, a projection lens, and an incident aperture, and enters into the EELS in the STEM. The EELS has such a structure that a magnetic sector in a fan shape serves as an electron spectrometer, a quadrupole electromagnetic lens and a hexapole electromagnetic lens are provided front and behind of it, and a parallel type electron beam detector is provided most downstream. The quadrupole electromagnetic lens is used for adjusting a focus of an electron energy loss spectrum, and magnifying the electron energy loss spectrum. The hexapole electromagnetic lens is used to reduce an aberration of the electron energy loss spectrum projected on the electron beam detector. The electron energy loss spectrum magnified by the quadrupole electromagnetic lens is projected on the electron beam detector, and the electron energy loss spectrum spanning a wide range is measured.
The electron beam detector comprises a scintillator receiving an electron beam and emitting fluorescence, and an element comprising multiple pixels for receiving the fluorescence. Alternately, it is a detector comprising multiple pixels for receiving an electron beam. The electron energy loss spectrum is measured based on the incident fluorescence or electron beam intensity.
Prior art relating to the structure of the EELS includes U.S. Pat. No. 4,743,756, Japanese application patent laid-open publication No. Hei 07-21966, Japanese application patent laid-open publication No. Hei 07-21967, and Japanese application patent laid-open publication No. Hei 07-29544.